Re: [PATCH v11 04/13] copy-on-read: pass overlay base node name to COR driver
On 14.10.2020 14:09, Max Reitz wrote:
On 12.10.20 19:43, Andrey Shinkevich wrote:
> We are going to use the COR-filter for a block-stream job.
> To limit COR operations by the base node in the backing chain during
> stream job, pass the name of overlay base node to the copy-on-read
> driver as base node itself may change due to possible concurrent jobs.
> The rest of the functionality will be implemented in the patch that
> follows.
>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich(a)virtuozzo.com>
> ---
> block/copy-on-read.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
Is there a reason why you didn’t add this option to QAPI (as part of a
yet-to-be-created BlockdevOptionsCor)? Because I’d really like it there.
I agree that passing a base overlay under the base option looks clumsy.
We could pass the base node name and find its overlay ourselves here in
cor_open(). In that case, we can use the existing QAPI.
The reason I used the existing QAPI is to make it easier for a user to
operate with the traditional options and to keep things simple. So, the
user shouldn't think what overlay or above-base node to pass.
If we introduce the specific BlockdevOptionsCor, what other options may
come with?
> diff --git a/block/copy-on-read.c b/block/copy-on-read.c
> index bcccf0f..c578b1b 100644
> --- a/block/copy-on-read.c
> +++ b/block/copy-on-read.c
> @@ -24,19 +24,24 @@
> #include "block/block_int.h"
> #include "qemu/module.h"
> #include "qapi/error.h"
> +#include "qapi/qmp/qerror.h"
> #include "qapi/qmp/qdict.h"
> #include "block/copy-on-read.h"
>
>
> typedef struct BDRVStateCOR {
> bool active;
> + BlockDriverState *base_overlay;
> } BDRVStateCOR;
>
>
> static int cor_open(BlockDriverState *bs, QDict *options, int flags,
> Error **errp)
> {
> + BlockDriverState *base_overlay = NULL;
> BDRVStateCOR *state = bs->opaque;
> + /* We need the base overlay node rather than the base itself */
> + const char *base_overlay_node = qdict_get_try_str(options, "base");
Shouldn’t it be called base-overlay or above-base then?
The base_overlay identifier is used below as the pointer to BS. The
base_overlay_node stands for the name of the node. I used that
identifier to differ between the types. And the above_base has another
meaning per block/stream.c - it can be a temporary filter with a JSON-name.
>
> bs->file = bdrv_open_child(NULL, options, "file", bs,
&child_of_bds,
> BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
> @@ -52,7 +57,16 @@ static int cor_open(BlockDriverState *bs, QDict *options, int
flags,
> ((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
> bs->file->bs->supported_zero_flags);
>
> + if (base_overlay_node) {
> + qdict_del(options, "base");
> + base_overlay = bdrv_lookup_bs(NULL, base_overlay_node, errp);
I think this is a use-after-free. The storage @base_overlay_node points
to belongs to a QString, which is referenced only by @options; so
deleting that element of @options should free that string.
Max
I will swap those two function calls (bdrv_lookup_bs(); qdict_del();).
Thank you.
Andrey
> + if (!base_overlay) {
> + error_setg(errp, QERR_BASE_NOT_FOUND, base_overlay_node);
> + return -EINVAL;
> + }
> + }
> state->active = true;
> + state->base_overlay = base_overlay;
>
> /*
> * We don't need to call bdrv_child_refresh_perms() now as the permissions
>